A four-year study of children in Baltimore and two other cities found that removing lead-contaminated soil from around homes did not reduce the risk of lead poisoning as much as had been expected, federal officials said yesterday.

The preliminary findings of the $17 million study raise new questions about the best way to attack a major public health problem. But the research seems to confirm the need to clean up lead-based paint inside older homes just as some landlords and real estate interests are trying to blame widespread poisoning mainly on lead in soil.

Lead-contaminated soil was believed to be one of the top sources of exposure for young children, who swallow an invisible but toxic dose of the metal in dust picked up on their hands. Officials estimate that more than half of the children under age 6 in the Baltimore area, and up to 4 million children nationwide, may have enough lead in their blood to suffer a drop in intelligence, learning disabilities and behavioral problems.

High lead levels have been measured in soil in yards in Baltimore and other cities. Much of that contamination comes from decades of automobile emissions before lead was removed from gasoline and from lead-based paint once widely used on homes.

The study, underwritten by the U.S. Environmental Protection Agency, found that removing lead-contaminated soil around homes yielded a small improvement in the health of children in Boston. But there were no significant gains for children in Baltimore or Cincinnati, said Larry G. Reed, an EPA official whose office supervised the research.

Mr. Reed summarized the results in an interview yesterday while attending an EPA-sponsored conference on the study in North Carolina.

In Baltimore, researchers studied 200 children living in 125 homes in lower Park Heights and Walbrook Junction. Topsoil with an average of 550 parts per million of lead was removed from around the Park Heights homes and replaced with clean dirt or sod. The soil was untouched in Walbrook Junction, for purposes of comparison.

The average lead level in the bloodstreams of the Baltimore children dropped from 10.9 micrograms per deciliter to 9.7 micrograms per deciliter, said Mr. Reed. Children are considered to have been poisoned if they have 10 micrograms or more of lead per deciliter of blood in their veins.

But the drop was too slight to be considered significant, and some children in the untreated neighborhood had greater reductions, said Dr. Katherine Farrell, a former Maryland Department of Environment official who reported on the study.

Advocates for children's health welcomed the results.

"It focuses us back again on paint and dust problems inside of homes as a way of controlling exposures," said Dr. Mark Farfel, a lead abatement researcher for the Kennedy-Krieger Institute in Baltimore. Almost 4 million homes nationwide have peeling and flaking lead-based paint, and about 500,000 homes in Maryland built before 1950 may contain lead paint.

"The bottom line is that lead in soil should not be used as an excuse for inaction in dealing with lead-based paint and dust hazards inside homes," said Don Ryan, executive director of the Alliance to End Childhood Lead Poisoning.